Thirty-one Stage III lung cancer patients with limited or extensive disease were studied for skin-test reactivity to a battery of five antigens, and for in vitro lymphocyte reactivity to these antigens and to the non-specific mitogen phytohemagglutinin (PHA) by a micro- radioassay, and for the production of migration inhibitory factor (MIF) in the presence of antigens. In patients with limited disease, 63% responded positively to two or more antigens, 31% to one antigen, and 6% to none; in patients with extensive disease, 40% responded to two or more, 47% to one and 13% to none. In vitro assays for antigen stimulation correlated with the skin- test results, using a stimulation index (S.I., the ratio of response in the presence of antigen or mitogen to the response in its absence) of 2.0 or greater and an inhibition of migration of 20.0% or greater as indicators of positivity. Mean S.I. to PHA for normals was 51.7 (plus or minus 10.9), while for patients with limited disease, it was 27.5 (plus or minus 18.8) and for those with extensive disease 21.8 (plus or minus 4.4). The MIF test in one case detected sensitivity to tuberculin PPD in a patient with an S.I. of 1.23 who was negative to intermediate strength skin-test activity, but proved to be positive when tested with second strength tuberculin PPD. It was shown that immunogenic RNA could be stored by lyophilization without loss of activity. Analysis of RNA integrity by electrophoresis in polyacrylamide-agarose gels was developed.